World’s Smallest Tic-Tac-Toe Game Built from DNA
Posted on by Dr. Francis Collins
Check out the world’s smallest board game, a nanoscale match of tic-tac-toe being played out in a test tube with X’s and O’s made of DNA. But the innovative approach you see demonstrated in this video is much more than fun and games. Ultimately, researchers hope to use this technology to build tiny DNA machines for a wide variety of biomedical applications.
Here’s how it works. By combining two relatively recent technologies, an NIH-funded team led by Lulu Qian, California Institute of Technology, Pasadena, CA, created a “swapping mechanism” that programs dynamic interactions between complex DNA nanostructures . The approach takes advantage of DNA’s modular structure, along with its tendency to self-assemble, based on the ability of the four letters of DNA’s chemical alphabet to pair up in an orderly fashion, A to T and C to G.
To make each of the X or O tiles in this game (displayed here in an animated cartoon version), researchers started with a single, long strand of DNA and many much shorter strands, called staples. When the sequence of DNA letters in each of those components is arranged just right, the longer strand will fold up into the desired 2D or 3D shape. This technique is called DNA origami because of its similarity to the ancient art of Japanese paper folding.
In the early days of DNA origami, researchers showed the technique could be used to produce miniature 2D images, such as a smiley face . Last year, the Caltech group got more sophisticated—using DNA origami to produce the world’s smallest reproduction of the Mona Lisa .
In the latest work, published in Nature Communications, Qian, Philip Petersen and Grigory Tikhomirov first mixed up a solution of nine blank DNA origami tiles in a test tube. Those DNA tiles assembled themselves into a tic-tac-toe grid. Next, two players took turns adding one of nine X or O DNA tiles into the solution. Each of the game pieces was programmed precisely to swap out only one of the tile positions on the original, blank grid, based on the DNA sequences positioned along its edges.
When the first match was over, player X had won! More importantly for future biomedical applications, the original, blank grid had been fully reconfigured into a new structure, built of all-new, DNA-constructed components. That achievement shows not only can researchers use DNA to build miniature objects, they can also use DNA to repair or reconfigure such objects.
Of course, the ultimate aim of this research isn’t to build games or reproduce famous works of art. Qian wants to see her DNA techniques used to produce tiny automated machines, capable of performing basic tasks on a molecular scale. In fact, her team already has used a similar approach to build nano-sized DNA robots, programmed to sort molecules in much the same way that a person might sort laundry . Such robots may prove useful in miniaturized approaches to drug discovery, development, manufacture, and/or delivery.
Another goal of the Caltech team is to demonstrate to the scientific community what’s possible with this leading-edge technology, in hopes that other researchers will pick up their innovative tools for their own applications. That would be a win-win for us all.
 Information-based autonomous reconfiguration in systems of DNA nanostructures. Petersen P, Tikhomirov G, Qian L. Nat Commun. 2018 Dec 18;9(1):5362
 Folding DNA to create nanoscale shapes and patterns. Rothemund PW. Nature. 2006 Mar 16;440(7082):297-302.
 Fractal assembly of micrometre-scale DNA origami arrays with arbitrary patterns. Tikhomirov G, Petersen P, Qian L. Nature. 2017 Dec 6;552(7683):67-71.
 A cargo-sorting DNA robot. Thubagere AJ, Li W, Johnson RF, Chen Z, Doroudi S, Lee YL, Izatt G, Wittman S, Srinivas N, Woods D, Winfree E, Qian L. Science. 2017 Sep 15;357(6356).
Paul Rothemund—DNA Origami: Folded DNA as a Building Material for Molecular Devices (Cal Tech, Pasadena)
The World’s Smallest Mona Lisa (Caltech)
Qian Lab (Caltech, Pasadena, CA)
NIH Support: National Institute of General Medical Sciences